#2018年省赛-程序设计题 付账问题
n, s = map(int, input().split())
a = list(map(int, input().split()))
avg = s / n  # 理论平均支付金额
a.sort()  # 让穷的人先付，升序处理能保证每个支付决策都是当前剩余系统的最优解
s2 = 0
for i in range(n):
    if a[i] * (n - i) < s:
        s2 += pow(avg - a[i], 2)
        s -= a[i]
    else:
        cur = s / (n - i)
        s2 += pow(cur - avg, 2) * (n - i)
        break

res = (s2 / n)**0.5
print("{:.4f}".format(res))
